In terms of environmental issues, aluminum and magnesium materials have been used in recent years for buildings, vehicles, etc. because of their lightweight and highly recyclable natures. These materials are generally joined by AC arc welding. However, in the case of applying AC arc welding to, for example, an aluminum material, arc interruption may occur when the polarity is switched from positive (the electrode is negative) to negative (the electrode is positive) or vice versa.
Arc interruption reduces workability, and also cools the melt pool, possibly causing weld defects. The conventional way to solve these problems is to regenerate the arc by applying a high-frequency high voltage between the electrode and the base material.
The operation of a conventional AC arc welding device to address arc interruption will be described as follows with reference to FIGS. 9 and 10. FIG. 9 is a schematic configuration view of the conventional AC arc welding device. FIG. 10 shows the change in welding control signals with time when arc interruption occurs during conventional AC arc welding control.
The operation of the AC arc welding device having the structure shown in FIG. 9 will be described with reference to FIG. 10. This is a non-consumable electrode AC arc welding device in which a positive-polarity period and a negative-polarity period are alternated.
In FIG. 9, AC arc welding device 1 includes welding output unit 2, AC frequency controller 3, current detection unit 4, arc interruption detecting unit 6, and high-voltage generator 16. Welding output unit 2 outputs a welding output. AC frequency controller 3 controls an AC frequency. Current detection unit 4 detects a welding current. Arc interruption detecting unit 6 detects arc interruption from the detection result of current detection unit 4. High-voltage generator 16 applies a high voltage between electrode 9 and base material 12. Electrode 9 is provided in welding torch 10. The welding output from welding output unit 2 is applied between electrode 9 and base material 12 so as to create arc 11 used for welding.
In FIG. 10, a time E1 is when the arc is extinguished, and a time E2 is when the arc is reignited.
In FIG. 9, welding output unit 2 includes primary and secondary inverters for alternating the positive-polarity period and the negative-polarity period based on the output of AC frequency controller 3. Welding output unit 2 receives commercial power (for example, three-phase 200V) from outside of AC arc welding device 1 and outputs welding voltage and current suitable for welding.
A negative polarity means that arc plasma electrons move in the direction from base material 12 to electrode 9, and that electrode 9 is positive, and base material 12 is negative. A positive polarity, on the other hand, means that arc plasma electrons move in the direction from electrode 9 to base material 12, and that electrode 9 is negative, and base material 12 is positive.
Current detection unit 4, which can be composed of a current transformer (CT), detects the welding current, and sets an arc interruption signal high when arc interruption occurs, and low when the arc is present.
Arc interruption detecting unit 6, which can be composed of a CPU, determines the occurrence of arc interruption from a current detection signal received from current detection unit 4.
AC frequency controller 3, which can be composed of a CPU, controls the welding output at a predetermined AC frequency, and outputs positive and negative control signals determined based on the AC frequency to welding output unit 2.
Welding output unit 2 includes IGBTs or other similar devices which switch the output polarity based on the positive and negative control signals. When the positive control signal is high, welding output unit 2 changes the output polarity such that electrons move from electrode 9 to base material 12, thereby providing the positive-polarity period. When the negative control signal is high, on the other hand, welding output unit 2 changes the output polarity such that electrons move from base material 12 to electrode 9, thereby providing the negative-polarity period.
The welding current and voltage from welding output unit 2 are supplied to welding torch 10 to create arc 11 between the tip of electrode 9 and base material 12 so as to perform AC arc welding.
High-voltage generator 16 applies a high frequency high voltage (generally, 12 kV) between electrode 9 and base material 12 when the arc interruption signal received from arc interruption detecting unit 6 is high. When the arc interruption signal is low, high-voltage generator 16 stops applying the high frequency high voltage.
As shown in FIG. 10, the arc interruption signal goes high at the time E1 when the arc is extinguished during normal welding. High-voltage generator 16 applies a high frequency high voltage (for example, 12 kV) to regenerate the arc between electrode 9 and base material 12.
Applying the high frequency high voltage between electrode 9 and base material 12 breaks the isolation between them, thereby regenerating the arc. At the time E2 when the arc is regenerated, high-voltage generator 16 stops applying the high frequency high voltage.
AC frequency controller 3 operates at an AC frequency predetermined for normal welding both while the arc is being interrupted and when the arc is present.
As described hereinbefore, according to the conventional method for performing AC arc welding using AC arc welding device 1, the arc is regenerated by applying a high frequency high voltage at the occurrence of arc interruption (see, for example, Patent Literature 1).
In this conventional method, however, the high frequency high voltage applied to reignite the arc at the occurrence of arc interruption may damage the surface of the weld bead or cause communication failure due to the high frequency high voltage.